The article studies on the design of cost control system of engineering project based on BP neural network. This paper identifies the black box of cost control with double and dynamic standards using BP neural network, analyzes the information sources, explains the influence of information sources to employee's cost control psychology and behavior, and determines specific inputs and outputs of cost control system with double and dynamic standards in manufacturing enterprise. This paper researches to evaluate the performance of cost control with double and dynamic standards and feedbacks the variances. Firstly, through analyzing the existing methods about performance evaluation of cost control, this paper chooses BP method as the basic performance evaluation methods of cost control with double and dynamic standards, and introduces the principles and typical models of BP method.